Many existing communication networks do not provide sufficient bandwidth to support real-time or near real-time presentation of content, such as videos, images or other large media files. The telephone network has been suggested as a means for transporting real-time content. However, systems using the public switched telephone network (PSTN) are often bandwidth limited, providing low quality presentation and services for content such as real-time video.
U.S. Pat. No. 5,410,343, assigned to Bell Atlantic Network Services, Inc., discloses a video-on-demand (VOD) system which relies upon telephone lines for distribution. Specifically, the system disclosed by the '343 patent uses asymmetric digital subscriber line (ADSL) channels, together with the public switched telephone network, for delivery of video program material. Generally, ADSL channels are bidirectional digital links having a high bandwidth downstream link and a low bandwidth upstream link. The advantage of ADSL is that higher bandwidth signals can be transmitted on ordinary telephone lines to end-user premises and additional cable or wiring is not necessary.
Although the system described in the '343 patent represents a significant improvement in the distribution of video programs, the system itself does not have sufficient downstream bandwidth to support high-quality VOD services, similar to those provided by digital broadcast service (DBS) providers. The downstream ADSL channel described in the '343 patent has a bandwidth of 1.544 Mbps, whereas contemporary digital cable service providers offer VOD services at bit rates ranging between 3-6 Mbps. The relatively limited bandwidth of the ADSL system does not permit real-time content at as high of quality as the digital cable and satellite broadcast systems.
U.S. Pat. No. 5,790,935, assigned to Hughes Aircraft Company, discloses a satellite-based digital broadcast system that provides virtual VOD services to subscribers. To reduce peak bandwidth demand, the system described in the '935 patent selectively downloads and caches digital files, such as videos, to subscriber units during off-peak hours. The disclosed system potentially improves the responsiveness of on-demand services by making some content locally available at subscriber units, without the need to access network resources. However, the '935 system requires content files to be stored in their entirety at the subscriber units. For large content files, such as videos, this requires larger storage devices in the subscriber units, and thus, increases the cost of subscriber units. Moreover, the '935 system does not utilize pre-existing network infrastructure, such as the PSTN, and instead relies on a wireless satellite communication network dedicated to video broadcast.
Accordingly, there is a need for an improved transfer system and method that permits the transport of real-time content over pre-existing networks, such as the PSTN.